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Stress tests for paints

Does paint still have the same glossy appearance after squeezing its way through all the pumps, pipelines and valves in the factory finish shops and finally reaching the component to which it is applied? A desk-sized miniaturized test facility can supply the answer.

Paints have to survive a long and arduous journey in factory finish shops before being transformed into the desired decorative coating. From the drums in which they are delivered, which may hold as much as 200 kilograms, the paints are conveyed through pipelines, pumps, valves and mixers until they reach the painting robot – a distance of up to a hundred meters. Exposure to this amount of stress means that many things can go wrong on the way. Sometimes the pigments undergo changes that alter the final color. Sometimes the filler component fails, and at worst the paint may separate into two phases. Even the adhesion properties and the brilliance of the paint can change. Before a company adopts a new paint system, therefore, its resistance to stress has to be tested. Which paints are suitable for industrial applications, and which should be avoided? How much solvent is needed to remove all traces of old paint from the plant? Some large companies own expensive test loops which can answer questions like these. But this usually exceeds the budget of small and medium-sized enterprises. It is with such users in mind that research scientists at the Fraunhofer Institutes for Manufacturing Engineering and Applied Materials Research IFAM in Bremen and for Environmental, Safety and Energy Technology UMSICHT in Oberhausen are developing a low-cost miniaturized test system which will be ready for use next year. The desk-sized reduced-scale facility is modeled on a 20-meter test loop equivalent to those used in factories. The researchers pump paint through this ring circuit and measure the temperature, pressure, flow speed and shear rate online. The decisive factor in the miniaturization of the test facility is that, despite the short distances, the paint must be subjected to exactly the same stress levels as in later everyday use. The researchers start by using simulations to calculate the shear values that occur in a full-scale plant. They then compare the results with data obtained from measurements made in the 20-meter test loop. Finally, they arrange the components that place the greatest stress on the paint in a linear configuration in the mini test facility – dispensing with pipelines and hoses that have little impact on the paint. Pumps, bottlenecks and pressure reducers create a flow profile as close as possible to that of a full-scale facility. “Instead of the usual 50 to 100 liters of paint, the new test system gets by with one or two liters. The miniaturized test setup not only costs less to buy but is also cheaper to operate and kinder to the environment,” says Buchbach.


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